The present invention relates to a method of manufacturing an electronic power component, and to an electronic power component obtained thereby.
Usually, an electronic power component, in particular one for use in the technical field of rail traction, comprises a substrate having a plurality of conductive layers applied thereto. At least one semiconductor power circuit is disposed on each of the layers, for example an insulated gate bipolar transistor (IGBT), or indeed a diode.
Each semiconductor circuit is provided on its face remote from the above-mentioned conductive face with metal connection tabs, and aluminum wires with a typical diameter of 380 microns (xcexcm) to 500 xcexcm being bonded thereto. Each of these wires is also bonded to one of the conductive layers covering the substrate.
That electronic power component, of known type, nevertheless suffers from various drawbacks. The above-mentioned aluminum wires give rise to numerous problems of reliability, associated with the mechanical stresses that act at the bonds between the wires and the corresponding connection tabs.
Furthermore, the wires give rise to parasitic inductance which can limit the performance of the electronic power component as a whole. Finally, the component does not optimize removal of heat, since heat can be removed through only one face of the component.
In order to resolve the above-mentioned drawbacks, at least to some extent, power connections have been proposed that do not make use of the above-mentioned aluminum wires. A manufacturing method has been implemented making use of pressed contacts, for example as described in EP-A-0 784 342.
Although that method of making components provides a solution that is satisfactory in terms of removing heat, it suffers from other drawbacks, in particular it requires complicated pressing mechanisms to be used. Furthermore, it is not convenient to implement insofar as it requires special semiconductor circuits.
In order to mitigate all of those drawbacks, the present invention seeks to propose a method of manufacturing an electronic power component, which method is simple and quick to implement while enabling an electronic component to be obtained that is robust and that guarantees satisfactory removal of heat.
To this end, the invention provides a method of manufacturing an electronic power component in which the following are placed in succession on a substrate: at least one conductive layer and at least one semiconductor power circuit, and in which metal connection tabs are fitted onto the face of the semiconductor circuit that faces away from the conductive layer, wherein the step which consists in applying said connection tabs to said face of the semiconductor circuit comprises a step of depositing a metal film by metallization, wherein at least one solder element is placed on the or each film obtained in this way, a conductive member is applied onto the or each solder element on its side remote from the metal film, and wherein the or each solder element is caused to melt so as to secure the or each conductive member with the or each metal film.
The invention makes it possible to achieve the above-mentioned objects.
The method of the invention makes use of manufacturing steps that are simple and easy to implement.
Furthermore, the component obtained thereby possesses improved reliability insofar as the bonding by soldering makes it possible to reduce to a significant extent the differential expansion that is inherent to prior use of metal connection wires.
Furthermore, the method of the invention provides satisfactory removal of heat from both opposite faces of each semiconductor circuit.
Finally, the method is of considerable flexibility insofar as it makes it possible to manufacture electronic power components using semiconductor circuits of different kinds, without major modification to the steps of the method.
In a first variant of the invention, the step of depositing the metal film is performed directly on a blank semiconductor die belonging to said semiconductor power circuit.
In a second variant of the invention, the step of depositing said metal film is performed on a preexisting connection member of said semiconductor circuit.
By way of example, such a connection member is constituted by a piece of aluminum foil covered in a layer of aluminum oxide. This implementation is advantageous given that it makes it possible to treat conventional prior art components, and even to upgrade used components.
According to another feature of the invention, the metal film is constituted by a titanium-nickel alloy.
According to another feature of the invention, the step of depositing the metal film is implemented by performing metallization through holes in a mask. This is advantageous in terms of manufacturing convenience insofar as the mask can be placed directly on the semiconductor circuit that is to be coated.
According to another feature of the invention, each solder element has a transverse dimension greater than 0.5 mm, and preferably greater than 1 mm. The term xe2x80x9ctransverse dimensionxe2x80x9d is used to mean either the diameter of the solder element, or else its greatest width.
In a first variant of the invention, each solder element is constituted by a preformed element, in particular a ball. This is advantageous, given that such preformed elements are easily stored. Furthermore, during manufacture of the power components, such stored preformed elements can be conveyed towards each metal film through openings in the mask as mentioned above.
In a second variant of the invention, each solder element is constituted by a measured-out quantity of solder.
According to another feature of the invention, each solder element is made of a tin-lead-silver alloy.
In a first implementation of the invention, the step of melting the or each solder element includes a primary melting stage for bonding each solder element to the metal film, the or each conductive member is then applied to the or each solder element after said primary stage, and a secondary melting stage is provided enabling each solder element to be secured to the corresponding conductive member. Once the primary melting stage has been performed, this implementation makes it possible to position each solder element in stable manner on the metal tab that it covers.
In a second implementation of the invention, each conductive member is applied to each solder element, and then said solder element is melted in a single step. This implementation is advantageous in terms of speed and simplicity.
According to another advantageous feature of the invention, each semiconductor power circuit is secured onto a corresponding conductive layer by interposing a film of solder between said circuit and said layer, and then by causing said film to melt, the film and each solder element being made out of the same material. This measure guarantees that implementation is highly convenient and gives rise to manufacturing costs that are low.
According to a particularly advantageous feature of the invention, both said solder film and each solder element are melted in a single step. By way of example, this melting is performed in an oven at a temperature lying in the range 180xc2x0 C. to 300xc2x0 C.
This measure serves to reduce the time required to manufacture the electronic component quite considerably. Each semiconductor circuit is secured in a single step on a corresponding conductive layer and simultaneously each conductive member is secured to the metal film with which the semiconductor circuit is provided.
The invention also provides an electronic power component comprising a substrate, at least one conductive layer supported by said substrate, and at least a first semiconductor power circuit placed on said conductive layer and having metal connection tabs secured via their faces facing away from the substrate to at least one conductive member, said component being made using the method as defined above.
According to other features of the invention:
the component includes at least two conductive members that are insulated from each other;
these two conductive members comprise an emitter and a grid, at least one of them being common to a plurality of semiconductor circuits placed on said substrate; and
the component further comprises at least one additional semiconductor circuit fitted onto the or each conductive member on its face facing away from said first semiconductor circuit.